A blue-violet semiconductor laser diode, made of Group III-V nitride semiconductors AlxGayIn1-x-yN (where 0≦x≦1 and 0≦y≦1) such as gallium nitride (GaN), is a key device that would enable optical disc drives to perform a write operation with extremely high densities, and is going to be introduced into actual products in increasing numbers. To develop new industrial fields of applications, it is indispensable to further increase the output power of such a blue-violet semiconductor laser diode because that would contribute to not only getting writing on optical discs done at even higher speeds but also applying it to laser displays.
Recently, a GaN substrate is expected to be more useful in making a nitride semiconductor light-emitting device than any other substrate. This is because a GaN substrate is superior to a conventional sapphire substrate in terms of the degree of lattice matching between crystals and heat dissipation property. What is more, although a sapphire substrate is electrically insulating, a GaN substrate is electrically conductive. This means that a structure in which current flows across the GaN substrate can be adopted by providing an electrode on the back surface of the GaN substrate. Also, if there is an electrode on the back surface of an electrically conductive GaN substrate, the size (i.e., chip area) of each semiconductor device can be reduced, which would increase the total number of chips that can be cut out of a single wafer, thus cutting down the manufacturing cost significantly. Actually, however, a significant quantity of heat would be generated when a light-emitting device such as a semiconductor laser diode is operated at high temperatures to provide high output power. That is why the light-emitting device should be accurately mounted on a heatsink.
Such a semiconductor laser, in which a light-emitting device (e.g., a semiconductor laser diode, among other things) that has been fabricated on a GaN substrate is mounted on a heatsink, is disclosed in Patent Documents Nos. 1 and 2, for example.                Patent Document No. 1: Japanese Patent No. 3650000        Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 2003-229631        